The present invention relates to an optical communication system using optical fibers and more particularly to an optical switch using a technique of microelectro mechanical systems (MEMS).
In an optical communication system, N×N optical switches are required at a relay point of communication network, which switches can connect arbitrary one of communication light beams transmitted to N input ports through optical fibers to arbitrary one of N output ports and can switch these connections freely. In the past, to meet this requirement, light beams have once been converted into electrical signals and after being subjected to switching, the electrical signals have been converted into light beams. In recent years, an optical switch has been developed which can perform switching of light beams while keeping them intact.
Available as a technique of optically monitoring optical connections in an optical switch is JP-A-2001-117025 based on U.S. application Ser. No. 09/414,621 filed on Oct. 8, 1999. The JP-A-2001-117025 discloses a configuration using optical translation units disposed before and after the optical switch. The optical translation unit is an appliance adapted to once convert a communication light beam into an electrical signal, confirm its intensity and waveform and thereafter reconvert the electrical signal into a communication light beam to transmit it to the optical switch, thus assuring the quality of the communication light beam. In the JP-A, electrical signals inside the optical translation units disposed before and after the optical switch are compared to each other and the attitude of moving mirrors is so controlled as to minimize the difference.
Highly accurate positioning is required of light beams incident upon output-side collimator lenses. In the event that a light beam deviates from the end face of an output-side collimator lens, optical coupling fails. Even when entering the end face of the output-side collimator lens, the light beam will fail to couple optically or a large loss will be incurred if its incident angle is outside a proper range. In the initial stage of assembling, collimator lens arrays and mirror arrays are positioned highly accurately.
However, as the temperature in the optical switch installation environment changes, the relative position between a collimator lens array and a mirror lens array changes and the optical coupling possibly fails even if predetermined attitudes of the moving mirrors are maintained. Otherwise, a large loss will possibly be incurred. Or, when the temperature in the optical switch system per se rises owing to continuous switching, the output of an electrical circuit changes and the moving mirrors will possibly fail to keep their predetermined attitudes.
In the method disclosed in the JP-A-2001-117025, the optical translation units before and after the optical switch are indispensable and disadvantageously, they make the construction complicated. Therefore, no reduction in the cost of the optical switch comes out. In addition, since two optical translation units are installed in respect of individual N ports, totaling 2N, and as a result, the size of equipment increases.